Physical barriers in the form of fences are used to surround various facilities ranging from private homes to government installations. One type of fence provides a physical barrier, or delay mechanism, which inhibits a potential intruder from gaining access to a protected zone. Such fences include chain link fences, and razor coil fences. Another type of fence provides both a physical barrier and an alarm, or detection, functionality. Such fences include pressure sensor taut wire fences and rigid fences in combination with vibration sensing modules. This latter type is generally referred to as part of a delay-and-detect type system since the fence provides both a delay and a detect function.
An inherent difficulty with delay-and-detect fences is the need to balance the quality of detection with adequate delay. An extreme example is a brick wall employed as a high quality delay mechanism with a vibration sensor fitted onto the wall. As may be appreciated, it would require substantial interference with the wall to trigger an alarm in such a system thus providing low detection quality. The opposite is also a problem, for example in a system which combines a flexible chain link fence with a vibrations sensor where sensitivity is increased but physical delay properties are reduced. Accordingly, present delay-and-detect systems employ reliable sensing element in a first system and then set the required delay quality by providing a physical barrier placed inward of the detection system. This allows for mounting additional fences, digging trenches, and placing other barriers which do not interfere with the detection functionality and increase delay quality. However, at times, geographic and aesthetic considerations do not allow for extending the width of the perimeter fence as far into the protected zone as is desirable for placing sufficient obstacles for a required delay. Other times, physical soil properties may inhibit the construction of separate supporting structures for a detect system and a delay system. For example, digging may be difficult by way of utility lines running under the fence perimeter. In those instances, it is very difficult to provide a delay element without compromising the sensing capability of the combined system. Accordingly, there is a need for a compact delay-and-detect system which can be deployed over restricted terrain while providing for reliable delay and detect functionality.